The present teachings relate to a radiation sensor including a photonic crystal structure and a method for fabricating the same. More particularly, the present teachings relate to a radiation sensor including a photonic crystal structure with improved transmission at a dielectric interface of the radiation sensor, and a method for fabricating the same.
Presently, two approaches are available to achieve improved transmission at a dielectric interface of a radiation sensor at the scintillator-photodetector boundary: (i) multi-layer coatings; and (ii) adiabatic transition in dielectric index.
Although multi-layer coatings (MLCs) are the standard approach, the bandwidth and range of angles over which transmission is improved depend on the number of layers and the precision in achieving the specified layer thicknesses. For moderate specifications. MLCs work quite well. For high-end applications where transmission must increase by large amounts over large bandwidths and angles of acceptance (“Omni-directional”), however, the manufacturing constraints and cost become prohibitive.
An alternative to MLCs is the use of a single layer whose effective index of refraction is specified by periodic “drilling” of subwavelength holes in a high-index medium substrate. Because the holes are smaller than the wavelength, they do not diffract or otherwise affect light transmission. The holes, however, reduce the effective index to a value much lower than that of the substrate.
Moreover, when a scintillator is coupled to a photodetector with a lower RI window, the light generated by the interaction of a γ-ray in the scintillator undergoes multiple total internal reflections and losses before exiting to the photodetector, limiting the light available for detection to only 30% of the total. This loss of signal degrades the energy resolution. The multiple total internal reflections in the scintillator also delay the exit of scintillation photons towards the photodetector, causing substantial degradation in timing resolution.